1. Field of the Invention
The present invention generally relates to metal-plated automobile wheels. More specifically, this invention relates to a composite automobile wheel having a permanently attached metal-plated overlay which is formed from a high impact plastic and whose bond strength with the metal plating permits the overlay to be shaped and contoured to closely conform to the shape of the wheel without concern for the deleterious effects of heat and corrosion on the high impact plastic or the integrity of the metal plating bond.
2. Description of the Prior Art
Motor vehicles often include substantial amounts of metal-plated trim elements which provide both decorative and functional purposes. In particular, chrome-plated aluminum wheels have been very popular since the time chromium plating was first introduced, and have recently become particularly fashionable with both sports cars and prestigious automobiles. Chrome-plated wheels are often significantly contoured to enhance their effect on the overall appearance of the vehicle by exploiting the highly reflective nature of the chromium surface.
However, automobile manufacturers have not generally provided chrome-plated cast aluminum wheels as original equipment on their automobiles because the porosity of the cast aluminum makes such wheels very difficult to plate. Moreover, the porosity of cast aluminum wheels results in a somewhat porous chromium plate layer which generally exhibits poor corrosion resistance to the wheel, causing the chromium plating to be susceptible to corrosion. Specifically, it is well known in the art that chrome-plated cast aluminum wheels have been unable to pass the automobile manufacturers' corrosion tests due to the inability of the copper-nickel-chrome layer to effectively cover the porous aluminum cast wheel. As a result, chrome-plated cast aluminum wheels have been provided to the public exclusively by aftermarket suppliers who adapt expensive plating techniques to attempt to solve this problem with limited success.
To obtain better plating results, current plating practices generally entail plating only machined surfaces of a cast aluminum wheel, the machining being intended to "close" the pores in the cast aluminum surface to promote a better subsurface to which the chromium may be plated. However, this approach severely limits the surfaces of a cast aluminum wheel which can be chrome-plated since known machining techniques are incapable of adequately machining deep recesses in cast aluminum wheels, such as the turbine openings formed in "spoke" wheels. Nevertheless, the entire wheel is often chrome-plated, resulting in poor adherence on surfaces which were not machined or inadequately machined, leaving these areas highly susceptible to delamination and corrosion. Chromium plating the entire wheel also incurs up to three pounds of additional weight, which detracts from the weight advantage of cast aluminum wheels.
In addition to the adverse effects of porosity and resulting corrosion, the adhesive strength of a chromium plating must be sufficient to endure deformation of the wheel as the automobile is driven down the road, or when the automobile is involved in a collision, or strikes road debris, roadway abutments or the like. Such hazards further challenge the ability of the chromium to adhere to the wheel without cracking or delamination. One known approach to avoiding this threat is to provide an ornamental wheel cover which is attached to the wheel so as to partially isolate the wheel cover from wheel deflections. U.S. Pat. No. 3,915,502 to Connell adopts this approach, providing an annular-shaped wheel cover that is permanently attached with double-sided adhesive tape to the wheel midway between the rim and the center hub area of the wheel. The remainder of the wheel cover is spaced apart from the outboard surface of the wheel, presumably to avoid the deleterious effects of heat generated by the tire, the wheel and the brake. However, Connell teaches nothing toward improving the subsurface of a metal-plating to the wheel cover such that the metal-plating might survive an automobile manufacturer's corrosion tests. In addition, the bulky structure taught by Connell almost completely hides or obscures the styling of a wheel, thereby significantly defeating the purpose of using a cast aluminum wheel--that is, the prestigious appeal associated with its appearance.
As another substitute for directly plating wheels, it is also known in the prior art to use a plastic overlay which is bonded to the outboard surface of the wheel for purposes of appearance and aesthetics. Generally, this approach is taken to allow the wheel to be designed for structural purposes, allowing the wheel's appearance to be determined by the ornamental design of the overlay.
As taught by U.S. Pat. No. 3,669,501 to Derleth, the ornamental surface of an annular-shaped overlay is a thin plastic cover, preferably formed from acrylonitrile-butadiene-styrene (ABS), which is axially spaced away from the outboard surface of the wheel to provide a cavity between the cover and the wheel into which an adherent polyurethane foam is disposed. Derleth teaches that the polyurethane foam adhesive provides a low-density, semi-resilient reinforcement for the thin gauge plastic cover while also providing sound insulation for tire and wind noise. However, it is understood by those skilled in the art that another reason for spacing the overlay's cover from the wheel surface is to avoid the deleterious effects of heat generated by the wheel and brake which would otherwise distort the plastic cover and delaminate any metal plating applied thereto. This is particularly true in the immediate region of the wheel hub where temperatures tend to be much higher than in the remainder of the wheel. As a result, definite styling and design limitations are associated with the use of the overlay taught by Derleth. Moreover, the styling of the wheel is obscured by the overlay. In addition, Derleth does not teach an overlay with improved adhesion between the overlay and its aesthetic treatments which might successfully pass an automobile manufacturer's corrosion tests.
Another example of an overlay is taught in U.S. Pat. No. 4,416,926 to Maglio, which discloses adhering a wheel cover to a wheel with a resin matrix containing hollow microspheres. Similar to the teachings of Connell and Derleth, the wheel cover taught by Maglio is also axially spaced away from the wheel to avoid the wheel's potentially high temperatures, particularly near the center of the wheel. U.S. Pat. No. 4,659,148 to Grill emphasizes this concern, teaching an overlay which is attached only to the outer regions of the wheel, while extending radially inward toward the center of the wheel a limited distance. A retainer is provided to space the overlay axially away from the center of the wheel, thus avoiding thermal conduction from the wheel center to the overlay. In contrast to Grill, U.S. Pat. No. 4,682,820 to Stalter teaches a plastic cap which completely covers but is axially spaced from the region of the wheel center. The cap relies upon an interference fit with an annular-shaped overlay to remain attached to the wheel.
In addition to their styling being significantly limited by the adverse effects of high temperatures, the ornamental plastic overlays of the above prior art all share a common disadvantage in their inability to permanently adhere a metal plating, particularly when exposed to a corrosive environment. Though the prior art fails to emphasize this aspect as a recurring problem, its existence is clear from the fact that automobile manufacturers have not to date provided chrome-plated plastic overlays as original equipment. As with the aforementioned chrome-plated wheels, metal-plated plastic overlays have been unable to pass the automobile manufacturers' corrosion tests, and therefore have been provided to the public exclusively by aftermarket suppliers.
A wide variety of platable plastics are known. For example, unmodified acrylonitrile-butadiene-styrene (ABS) has been plated to provide decorative articles such as headlamp surrounds, and plumbing and marine hardware. Unmodified polycarbonate (PC) has been utilized as the substrate for plated motor vehicle door handles. In addition, several other plastics have been successfully plated for various decorative purposes. However, these plastics, even though platable, do not provide a satisfactory substrate if the finished article must be capable of sustaining significant impacts or temperatures. Accordingly, the use of these materials within an automobile is limited. These plated plastics are characterized by a tendency to fail at low energy levels of impact, resulting in the delamination of the chromium plating from its plastic substrate. In addition, as an extreme example, the unmodified ABS may even shatter upon impact. Thus, for a plastic to be suitable as a substrate for a metal-plated wheel cover or overlay, the adhesion between the plating and the substrate must generally have sufficient impact resistance, as well as temperature and corrosion resistance.
From the above discussion, it can be readily appreciated that the prior art does not disclose a metal-plated cast aluminum wheel whose metal plating is provided uniformly over the surface of the wheel, including the contours and deep recesses of the wheel, while also being capable of passing an automobile manufacturer's corrosion resistance test. In addition, the prior art does not disclose a metal-plated overlay which can be permanently adhered directly to the wheel to closely follow the contours of the wheel while also being resistant to delamination of the metal plating due to corrosion, high temperatures and impact. In effect, the design requirements of such overlays restrict the location of the overlays on the surface of the wheel, while also limiting the appearance of the overlay by requiring that the metal-plated surface be axially spaced and isolated from the outboard surface of the wheel to avoid the adverse effects of the elevated wheel temperatures. Finally, the prior art has not provided a metal-plated overlay which permits the cast aluminum wheel to define the overall styling and structural appearance of the wheel, while the overlay is specifically limited to contributing the reflective character of the wheel for purposes of aesthetics.
Accordingly, what is needed is a low-cost ornamental metal-plated overlay for an automobile wheel which can be permanently secured directly to the wheel to closely follow the contours of the wheel, without needing to insulate the metal-plated surface of the overlay from the wheel and without needing to drastically limit the location of the overlay such that the overlay is isolated from the center and periphery of the wheel. As a result, styling and design flexibility would be enhanced because the overlay would be capable of closely conforming to the contours of the entire wheel surface. As such, the wheel would be permitted to define the outward styling configuration of the wheel while the overlay provides the aesthetically-pleasing reflective appearance. In addition, a metal plating or colorful paint on such an overlay would remain securely adhered to the overlay, even when exposed to adverse physical, chemical and thermal attack.